Heretofore, in a membrane electrode assembly (MEA) of a solid oxide fuel cell, there has been known a multilayer structure in which electrode structures (three-phase structures), each being formed of a catalyst in which platinum is supported on carbon particles and of ionomer, are bonded to both sides of an electrolyte membrane, and further, gas diffusion layers are arranged thereon.
For electrode catalyst layers of the three-phase structure, it has been proposed to enhance drainage thereof by adding a water-repellent agent such as polytetrafluoroethylene (PTFE) to the electrode catalyst layers, by using highly hydrophobic carbon black and carbon black subjected to hydrophobic treatment, and so on (refer to Japanese Patent Unexamined Publication No. S59-43889).